Electric lamp with concentrated light source



July 9, 1935. R. HARDING, JR 2,007,945

ELECTRIC LAMP WITH CONCENTRATED LIGHT SOURCE Filed Sept. 16, 1950 l NVENTOR fFosz/Pr/flia/lvqlii ATTORNEY Patented July 9, 1935 2,007,945

UNITED STATES PATENT OFFICE ELECTRIC LAMP WITH CONCENTRATED LIGHT SOURCE Robert Harding, Jr., Elmsiord, N. Y., assignmto Sirian Lamp Company, Newark, N. J., a corporation of Delaware Application September 16, 1930, Serial No. 482,243 Claims. (Cl. 1761) This invention relates to electric lamps of the as Nernst or Welsbach material may be supgaseous discharge type. ported by any suitable means such as by two In the application of Chester H. Braselton, rods 13 and H which may extend into the ends entitled Electrical discharge device, Serial No. of the cylinder as indicated in Fig. 2. The rods 5 459,048, filed June 3, 1930, an electric lamp is l3 and I4 may be welded respectively to support 5 described in which an electron emitting element rods l5 and I 6 which may extend downwardly is heated by passing a current therethrough in to the press I I in which they may be sealed. the presence of an ionizable gas at a pressure Leading-in wires l1 and I! may be connected suificient to confine the ionization of the gas to respectively to the support rods l5 and I 6.

10 the region of the electron emitting element. The cylinder 12 is preferably provided with a 10 When the electron emitting element is enerhelical groove l9 which extends around the cirgized a brilliant bluish-white discharge in the cumference from end to end forming a helical nature of a halo appears along the electron wall 20 the sides of which are separated by the emitting element forming a conductive path outp c g o the E V Around the groove is I side of the element and producing a bright uniwind an electron emitting element 2| which may 15 form light. In this device, however, a reslstbe made of a coil 22 of resistance wire closely ance wire is necessary and it is somewhat dimwound in concentrated form and the outer surcult to get a resistance wire which will be heated face of which s ated with an el c ron emittin to the correct temperature and have the proper materiel The resistance wire y be y resistance when used with 110 volts so that a desired l'esistenee wire Such as tungsten, y 20 relatively long filament may be necessary to take mlm, tantalum. h m d the r n the voltage. This necessitates a spreading out emitting material 13 ay b y of e w of the light source over a relatively large area. known meterieleused for that p p e ch as It is therefore one of the objects of the present the oxides of the alkaline earth metal p, all

25 invention to provide an electric gaseous discharge of which a an electron emissivity when heated 25 lamp with a concentrated li ht r in excess of that of thorium oxide, or mixtures Another object of the invention is to provide of such materials but preferably the ma an electric lamp in which illumination is proshould include one which has the p ope y of duced not. only by a gaseous discharge but by selective radiation such as calcium oxide. Where radiation from a refractory member which is the ends the element 2| extend y d the 30 heated by the discharge, ends of the cylinder i2 they may be welded to the Another object of the invention is to provide Support rods 15 a to c i y connect the an electric lamp in which a refractory member Support rods with the element ls used to guide an ionic discharge so as to greatly The bulb is filled w a inert gas 1 mixt r increase the length of the discharge for a given of such gases Preferably th se having 8. mon- 35 space. atomic structure such as neon, argon, helium,

Other objects of the invention and objects krypton. Xenon, and the like- Also vapors of relating particularly to the construction and asmete-1S h as mercury, caesium, or rubidium sembling of the various parts will be apparent may be mixed in small quantities with the other an as the description of the invention proceeds. gases to increase the conductivity d o p duce 40 Several embodiments of the invention have 00101 effectsbeen illustrated in the accompanying drawing in metal vapor may be introduced int he which: bulb by providing a salt such as a chloride, of Fig. 1 is a side elevational view of my imthe desired metal together with a a l q y 5 proved electric lamp; of magnesium in a suitable container |5a which Fig. 2 is an enlarged longitudinal sectional may e moun d y means f the wire l5b up view of the elements sho n in i 1; the support rod l5. When this containerisheat- Fig. 3 is an enlarged longitudinal sectional view d y external me t aft r he bulb is of the electron emitting element; and sealed oil the magnesium flashes and forms mag- Fig. 4 is a longitudinal sectional view of a, nesium chloride liberating the other metal which 50 modified form of electron emitting element. conde ses 0n the nner walls of the bulb. It

The lamp shown in Fig. 1 comprises an envelevaporates again as soon as the bulb is heated in ope M, which may be formed integral with the use. usual press I l for supporting the elements of the When the current is turned on current will flow lamp. A cylinder l2 of refractory material such through the leading-in wire 11, hr g he 111 55 port rod $5, the element H, the support rod l0. and out through the leading-in wire it. This energizes the element 2i and raises the temperature thereof so that it becomes a. good electron emitter. The bombardment of the gas by the electrons apparently causes ionization thereoi which produces a conductive path in the region of the element so that current will flow from one end of the element to the other along this conductive path. Inasmuch as the adjacent turns of the element are separated by the wall 20 of refractory material there can be no short circuit of the discharge from one turn to another except over the edge oi the wall 2t. When the ionic discharge appears it bombards the wall 26 and raises the temperature thereof until the refractory material radiates light and increases the total light output oi the lamp. As the surface only is bombarded and as it is the surface that emits light there is no temperature drop through the refractory mate rial and more energy is therefore translated into light.

When the discharge appears and the cylinder it becomes heated it also acts as a conductor of electricity and a current will thenfiow through the cylinder i2 between the rods i3 and it. This helps increase the temperature of the rod i2 but the large percentage of the current will flow in the element 2i and around the groove it following the path of the low resistance ionized gas in the vicinity of the element. I

Care should be taken in exhausting the lamp that substantially all occluded gases are removed and pure gases are used to fillv the envelope. With the elements mounted as in Fig. 1 upon the press ii and the press sealed in the envelope iii, the latter may-be connected with a vacuum pump and covered by the usual oven for raising the temperature thereof to about 350 to 400 C. or to as high a temperature as the glass will stand without deforming. Sufiicient current may be run through the filament at this time to raise the temperature thereof to approximately 600 C. and the heating and evacuating are continued until there is no fluorescence when high tension current from an induction coil is directed against the walls of the bulb or in other words until there is no more gas inside of the bulb. This process may be continued until a high vacuum of about .5 micron is obtained. The current may then be increased through the filament and the temperature thereof slowly raised until it is a bright red at a temperature of about 800 C. This drives out the binder in the electron emitting material and other occluded gases which might be present.

When no more gas is found in the bulb the oven may then be raised and the filament heated for a.

,moment to about 1200 C. the pump being connected all this time to maintain a high vacuum. The pump may then be shut off and the filament current turned off and a slight amount of inert gas preferably neon at about mm. pressure admitted into the bulb and the filament current then turned on again. Spots of localized discharge having a reddish color will then appear. These spots gradually spread until a, diffused glow completely fills the bulb. This process appears to activate the electron emitting coating and is maintained until the discharge is uniform throughout the entire bulb which usually takes less than ten minutes when the activation is completed. During this time the current on the filament should not be raised too high so the coating will not be destroyed or thrown off from the filament.

If white discharge spots appear on the filament or the support rods, it is an indication that there are more gases or vapors in the bulb and the bulb is again preferably exhausted and the whole process of activation repeated.

When the activation is completed the filament temperature may be raised to about 1400 0., then the vacuum pump again connected and the gas pumped out to remove the undesirable gases which may have been thrown ofi during the activation process. The filament circuit may then be disconnnected, the pump turned ofi, and about 50 mm of neon gas followed by about 150 mm of argon may be admitted into the bulb. The bulb may then be sealed ofi and is ready for use.

It will be noted that the light is produced from several sources: the light produced by the filament itself, the light produced by the discharge which surrounds the filament, and the light produced by the refractory cylinder 92, and it will be noted that inasmuch as the electron emitting element is wound around the cylinder it the space taken up is relatively small compared to the space it would take if the filament were stretched out in a straight line. Thus the region of the light source is reduced to a minimum.

It may be desirable instead of using a coii or resistance wire, as indicated in Fig. 3-, to

single wire which may be wound around a smaller groove 25 provided in a refractory cylinder 26. If desired the wire 2% may be coated with electron emitting material before winding in the groove or it may be wound first and the outer surface coated as indicated in Fig. 4.

If desired the pressure in the bulb may be made sufiicient so that there will be no discharge over the top of thewall 20 but the discharge will then be confined to a spiral path around the groove it. However, the invention is intended to contemplate the extension of the discharge far enough outwardly to permit short circuiting across the wall 20.

Many modifications of the invention may be resorted to without departing from the spirit thereof, and I do not therefore, desire to limit myself to what has been shown and described except as such limitations occur in the appended claims.

What I claim is:

1. An electric lamp comprising an envelope, an electron emitting element within said envelope so bent that portions thereof are nearer together across a gaseous space than along the conducting path of said element, the density of electron emission when heated being in excess of that from thorium oxide, an ionizable gas sur-- rounding said element and having a breakdown potential per unit length of element less than the potential along said unit length of element necessary to raise said element to electron emitting temperature, and means between said portions to hinder a current flow between said portions through said gas.

2. An electric lamp comprising an envelope, an electron emitting element within said envelope,

the density of electron emission when heated means between portions of said element to limit flow oi. current from one portion to the other through contact from adjacent layers of ionized gas, said electron emitting element forming the sole source oi the discharge.

3. An electric lamp comprising an envelope. an electron emitting element within said envelope, the density 01' electron emission when heated being in excess of that from heated thorium oxide, an ionizable gas surrounding said element and having a breakdown potential per unit length of said element only when said element is subjected to electron bombardment which is less than the potential along said unit length necessary to raise said element to electron emitting temperature whereby a layer of ionized gases is formed about the element when heated, and means to separate the ionized gas layer adjacent one portion of said element from the ionized layer of gas adjacent another portion of said element to prevent a current discharge between said two portions through said gas layer, said electron emitting element forming the sole source of the discharge. 7

4. An electric lamp comprising an envelope, an electron emitting element containing an oxide 01' the alkaline earth metal group within said envelope wound in the form of a coil, an ionizable gas surrounding said element and having a pressure sumcient to confine the ionization of said gas to the region 01 said element when said element is energized, and means-between the turns of said coil to hinder a direct current path from one turn to another on the exterior of said coil when said filament is energized, said electron emitting element forming the sole source of the discharge.

5. An electric lamp comprising an envelope, a cylinder of refractory material within said envelope having the quality of selective radiation, a helical groove around the circumference oi the cylinder, a filamentary resistance wire wound in said groove, a coating oi! an oxide of one of the alkali earth metals on said wire, the diameter of said wire and the coating being less than the depth of said groove, and an ionizable gas containing a mixture of neon and argon surrounding said wire and element and having a pressure sufilcient to confine the ionization of said gas to the region 0! said wire when said wire is energized, whereby a layer oi. luminous gas is formed about the external surface of said cylinder, said coated resistance wire forming the sole source of the discharge.

- ROBERT HARDING, Jr. 

